This section provides background information related to the present disclosure which is not necessarily prior art.
Automatic transmissions provide a plurality of forward and reverse speed or gear ratios by selectively actuating one or more clutches and/or brakes to establish a torque-transmitting drive connection between a transmission input and a transmission output for supplying motive power (i.e., drive torque) from a powertrain to a driveline in a motor vehicle. One type of brake or clutch widely used in automatic transmission is an overrunning coupling device, commonly referred to as a one-way clutch (OWC), which overruns when one of its races (in radial coupling configuration) or one of its drive plates (in axial coupling configurations) rotates in a first (i.e., freewheel) direction relative to the other race or drive plate, and engages or locks in a second (i.e., lockup) direction. Such conventional overrunning coupling devices provide no independent control over their modes of operation, that is to say whether they lockup or freewheel in both directions. Thus, basic one-way clutches provide a “locked” mode in one rotary direction and a “freewheel” mode in the opposite direction based on the direction that the drive torque is being applied to the input race or drive plate.
There are however, requirements in modern automatic transmissions where a “controllable” overrunning coupling device, commonly referred to as a selectable one-way clutch (SOWC), can be selectively controlled to provide additional functional modes of operation. Specifically, a selectable one-way clutch may further be capable of providing a freewheel mode in both rotary directions until a command signal (i.e., from the transmission controller) causes a power-operated actuator to shift the coupling device into its lockup mode. Thus, a selectable one-way clutch may be capable of providing a drive connection between an input member and an output member in one or both rotational directions and it may also be operable to freewheel in one or both directions.
In some instances, the selectable one-way clutches installed in automatic transmissions utilize a hydraulic actuator to selectively actuate the overrunning coupling and shift between the available operating modes. Examples of conventional selectable one-way clutches that are hydraulically-actuated are disclosed in U.S. Pat. Nos. 6,290,044, 8,079,453 and 8,491,439. In contrast, it is also known to use an electro-mechanical actuator with the selectable one-way clutch, one example of which is disclosed in U.S. Pat. No. 8,196,724.
As a further alternative, much development has recently been directed to electromagnetic actuators for use with selectable one-way clutches, examples of which are disclosed in U.S. Pat. Nos. 8,276,725 and 8,418,825 and U.S. Publication 2013/0319810. In most electromagnetic actuators, a rocker-type locking element, commonly referred to as a strut, is pivoted from a first position to a second position in response to energization of a coil assembly. In most conventional selectable one-way clutches equipped with an electromagnetic actuator, a direct-acting configuration is used such that the strut is part of the magnetic circuit and its pivotal movement is caused by an attraction force applied directly to the strut via energization of the coil assembly. Therefore, precise control of the air gap established between the core/pole piece of the coil assembly and the strut is required to provide robust and reliable lockup functionality.
While all of the different types of selectable one-way clutches mentioned above appear to meet all functional requirements, a need exists to continue development of new and improved power-operated actuators that advance the art and provide enhanced functionality.